Method of removing nickel and cobalt impurities from zinc electrolyte solutions



Patented May 30, 1950 UNITED STATES METHGD OF REMOVING: NECKEL AND CO BALT. IMRUEITIES FRGM ZINC ELECTRO- LYTE SOLU'EIONS Dinsmore Laurence Grifiith and Mavis Jean Rankin, *Flin Fion, Manitoba, Canada, assignors to re @T OFFICE Hudson Bay Mining and smelting 00., Limited, Winnipeg, Manitoba, Canada No Drawing.- Application Marchb, 1946, Serial No. 652,246

4Ciaims.

1 This invention relates to the removal of impurities present in zinc electrolyte solutions prior to the recovery of zinc therefrom by the electrolytic method, and it is directed particularly to as cobalt and nickel and this is illustrated by the following experiment which was carried out with a sample of tankhouse electrolyte (electrolyte ready for electrolysisin the hydro-metallurthe removal of cobaltandnickel from suchsolu- 5 gical process for winning, zinc) having the foltions. lowing analysis:

It is well known that impurities inthe electro-= D u lyte cause great difiiculty during the operationof 33 gf 'fif plating by electrical methods, in somecases due p f g s p to the impurity itself platingand so causing the 6 I i i 1 deposit to be impure andof less value, and in ggj 0 6 other cases due to the impurity 'bringingyabouta A loweredeffi'ciency in the plating process. Consen lmony q y re p ins re k n d m h xpens inc dust and copper were then added to this is incurred in removing the harmful impurities electrolyte, using the normal small amounts, so far as possible. namely, 5 grams per litre ofzincdust and 1.4%

Ithas for many years been known that purigrams per litre of copper as copper sulphate. fication of an electrolyte may be eiiected by the Ehen purification tests were run on. samples of displacement of one metal from the solution by this electrolyte with additions of arsenic (as another higher in the electromotive series and 20 arsenious oxide dissolved in sodium hydroxide that such a displacement may be aided by the and water, and neutralized to methyl orange presence of a metal low in the electromotive with sulphuric acid) as set forth below, the series. Thus it is common, after iron and other samples being agitated for'one' hourat 45 C. metals have been precipitated by treating an elec- The analyses of the filtrates from these tests trolyte with zinc oxide or roasted zinc ore or were as follows: lime whileair-is-blown through the solution, to treat it with zinc dust andto increase the purifyingactionof the zinc dust by coating it with finely l i g divided copper. This copper is commonly formed Test Extra Addiims by precipitating it from the solution to be purified Cu 0d 00 As Sb by the zinc dust.

On the basis of the above generalization as to 111; .51; 1,0; 022 removal of one metal in solution by another $18 8:832 metal higher in the electromotive series, and this 12.9 20.0 0. 028 removal being aided by the presence of a metal 10W in the electromotive series, one would expect We have discovered that surprisingly good that all of the impurities could be removed withresults are Obtained in the removal of impurities out serious difficulties. Experiments have shown, and particularly cobalt if Small amounts of both however, that certain elements such as cobalt and Silver and arsenic in the form of mm nickel, which Should, from the Position assigned pounds are present in addition to the normal to them in the electromotive series, easily be small amounts of zinc dust and a soluble copper removed, are exceedingly difficult to precipitate, compound. The amount of Silver to be added the d fi y becoming m pronounced as the varies according to the concentration of impuriqllalltity 0f the p r es present in the electroties in the particular electrolyte to be purified l e be es ss- Thus, it has n e possible and precise directions as to the addition required to remove e than a few milligrams pe litre, for a given degree of purification may, therefore, s y r about 15 d w to a t 10 mill rams not be stated. However, tests made on samples P litre, of Such pu s s cobalt a d n l, of tankhouse electrolyte show that remarkably and much Work has been done to determine good results are obtained with as little as 100 methods of removing these and other impurities milligrams per litre of silver and that about 500 which are similarly diflicult to precipitate, milligrams per litre is usually sufiicient to reduce It has been proposed to use arsenic with zinc cobalt and nickel present as impurities to very dust and copper but we have found that zinc small amounts. dust, copper and arsenic additions alone are of Thus 250 milligrams per litre of silver in the little, if any, value in removing impurities such form of silver sulphate crystals with milli- 3 grams per litre of arsenic made cobalt not detectable in a sample of tankhouse electrolyte of the following analysis:

Zinc "grams per litre About 120 Copper milligrams per litre 0.4 Cadmium do 0.9 Cobalt .do 16.5 Arsenic do 0.02 Antimony do 0.028

The additions of zinc dust and copper were as set forth above and, after agitation for one hour at 45 C., the analysis of the filtrate in milligrams per litre was as follows:

Cu Cd As Sb 1 Not detectable.

' The addition of silver as well as zinc dust, copper and arsenic also lead to very good results in the removal of nickel. Thus 500 milligrams per litre of silver as silver sulphate and 175 milligrams per litre of arsenic in sulphuric acid solution together with zinc dust and copper, as set forth above, were added to a sample of tankhouse electrolyte of the following analysis:

Zinc "grams per litre 135 Cadmium milligrams per litre 0.4 Antimony do 0.02 Copper do 0.5 Arsenic do 0.02 Cobalt d0 23.6 Nickel do 18.8

After agitation for one hour at 40 C., the analysis of the filtrate in milligrams per litre was:

Milligrams per litre Nickel 1.8 Cobalt 1.2

Other tests carried out showed that bismuth, gold, iron, cadmium, mercury, chromium, molybdenum, phosphorus, gallium, tungsten, sulphur, tellurium, germanium, selenium, nickel, palladium and platinum are, amongst others, of no value along with zinc dust, copper and arsenic; indeed certain of these metals, as for example platinum, are very detrimental, since not only is cobalt not removed, but the solution is left high in copper and arsenic.

What we claim as our invention is:

1. A method of removing impurities from zinc electrolyte, comprising contacting the electrolyte with small amounts of zinc dust, in the presence of small amounts of soluble copper, arsenic and silver compounds.

2. A method of removing impurities from zinc electrolyte solutions, comprising contacting the electrolyte with small amounts of zinc dust, in the presence of small amounts of soluble copper and arsenic compounds and from about to about 500 milligrams per litre of silver in the form of a soluble compound.

3. A method of removing impurities from zinc electrolyte solutions, comprising adding to the electrolyte small amounts of zinc dust, copper sulphate, a soluble arsenic compound and a soluble silver compound.

4. A method of removing impurities from zinc electrolyte solutions comprising adding to the electrolyte small amounts of zinc dust, copper sulphate, a soluble arsenic compound and from about 100 to 500 miligrams per litre of silver in the form of a soluble compound.

DINSMORE LAURENCE GRIFFITH. MAVIS JEAN RANKIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,403,065 Avery et al. Jan. 10, 1922 1,733,676 Stevens et al. Oct. 29, 1929 2,396,569 Griflith et a1. Mar. 12, 1946 

4. A METHOD OF REMOVING IMPURITIES FROM ZINC ELECTROLYTE SOLUTIONS COMPRISING ADDING TO THE ELECTROLYTE SMALL AMOUNTS OF ZINC DUST, COPPER SULPHATE, A SOLUBLE ARSENIC COMPOUND AND FROM ABOUT 100 TO 500 MILIGRAMS PER LITRE OF SILVER IN THE FORM OF A SOLUBLE COMPOUND. 